Figure 3.

Reporter activity in vivo. β-galactosidase activity (Miller units) is shown on a logarithmic scale (y-axis) as a function of the center-to-center spacing (x-axis) between promoter and downstream O₁ operator. Data from 89.5 bp (blue circles) and 100.5 bp (red triangles) constructs are shown in the absence (open symbols, dashed black fit line) and presence (filled symbols, solid black fit line) of IPTG induction. Average reporter activities of promoter constructs with an isolated downstream O₁ operator in the absence (dashed gray) and presence (solid gray) of IPTG are shown. Similarly, average reporter activities for promoter constructs with an isolated upstream O_sym operator in the absence or presence of IPTG fall in the gray shaded region of the graph. Black lines show best fits to a thermodynamic model of promoter accessibility.